This is "Saint Francis of Assisi with Angels" by Sandro Botticelli. Painted in the Italian north, it's a beautiful example of early Renaissance art. The saint stands on a marble ledge against a golden background, embracing a Crucifix and gazing compassionately at the tiny figure of the crucified Christ.
If you look closely, you can see bright red blood on Christ's feet and his white loin cloth, where it has dripped from the wound in his side. The saint is flanked by angels playing musical instruments, their feet supported by small clouds. His meditation on Christ's suffering was so intense that he miraculously developed the wounds of the Crucifixion.
These stigmata are visible here on his hands and feet, and it's said that Saint Francis's intense identification with the suffering of Christ led him to become known as the alter Christus, or 'another Christ'. This empathetic devotion was the hallmark of Franciscan spirituality, and this picture probably made for private worship encourages emulation of his piety and devotion.
The painting is unusual for Botticelli, who usually painted fragments of larger works. The gold background, however, is a striking feature, with its textured surface created by incising and punching to create a diamond pattern. This would have glimmered and sparkled in candlelight, intensifying the glory and mystery of the saint's vision.
Saint Francis of Assisi with Angels hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.